86 SWEETENED CONDENSED M1t,.K—CONDENSING 
Rapid evaporation cannot take place until the milk is brought 
to the boiling point and is kept there until evaporation 1s com- 
pleted. Under atmospheric pressure and at the sea level, the 
boiling point of water is 212 degrees I*., the boiling point of milk 
is very slightly higher, about 214 degrees F. Evaporation of milk 
under atmospheric pressure in an open kettle, however, is a 
relatively slow process, requiring a long time and large appara- 
tus. Furthermore, exposure of the milk to 212 to 214 degrees 
F. long enough to complete evaporation would render the prod- 
uct unsuitable for market. ‘The properties of some of its ingre- 
dients are altered, the product would assume a dark color and 
a marked cooked flavor as the result of the effect of heat. All 
of these objections are minimized and partly avoided by-lower- 
ing the boiling point of milk. These objections, however, do 
not apply to evaporation under atmospheric pressure by film 
treatment, as is the case with the Continuous Concentrator de- 
scribed in Chapter XIV. 
Relation of Pressure to Boiling Point.—-The temperature at 
which milk boils depends on the pressure to which it is exposed. 
